HK1108317B - Semisynthesis process for the preparation of 10-deacetyl-n-debenzoyl-paclitaxel - Google Patents

Description

Semi-synthetic process for the preparation of 10-deacetyl-N-debenzoyl-taxol

Technical Field

The object of the present invention is a new semi-synthetic process for the preparation of 10-deacetyl-N-debenzoyl-paclitaxel (I), a useful synthon for the preparation of taxanes with antitumor activity.

The invention also relates to a process for the preparation of 10-deacetyl-di-7, 10-trichloroacetylbaccatin III, in which less than 0.1% of the corresponding 7 or 10 mono-trichloroacetyl derivative is present, as determined by HPLC.

The present invention also relates to a process for the preparation of docetaxel having a purity higher than 99% obtained by reacting the intermediate (I) obtained by the process of the present invention with di-tert-butyl dicarbonate, and a pharmaceutical composition comprising said high purity docetaxel.

Background

In WO 94/07877 it is disclosed to include an oxazolidine of formula (II)

With 10-deacetylbaccatin of formula (III) protected in the 7-and 10-positions

Carrying out an esterification reaction to give an ester of the formula (IV)

The synthon (I) of (1), which was reported in the early nineties in the literature (F. Guerette-Voegelein et al, J. Med. chem.34, 992, 1991).

The liberation of the amino function at the 3 'position and the hydroxyl groups at the 2', 7 and 10 positions of the ester of formula (IV) provides synthon (I).

In particular, according to the above-cited patent application, the radical R may be hydrogen, alkyl, alkoxy or a number of substituted phenyl radicals, and R₁Is an alkyl group substituted with one or more chlorine atoms. The group G is alkylsilyl or R₁-O-CO group, wherein R₁As defined above.

Starting from the intermediate of formula (IV), the hydroxyl and amino functions are freed by reduction with zinc and an acid, and when the group G is an alkylsilyl group, the free hydroxyl function is treated by acid treatment, for example with hydrofluoric acid.

Summary of The Invention

The present invention, in its first embodiment, relates to a process for the preparation of 10-deacetyl-N-debenzoyl-paclitaxel (I),

the method comprises the following steps:

a) 2- (2, 4-dimethoxyphenyl) -3- (2-nitrobenzenethiol) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid (V)

With 10-deacetyl-di-7, 10-trichloroacetylbaccatin III (VI)

The reaction is carried out to obtain 2- (2, 4-dimethoxyphenyl) -3- (2-nitrobenzenesulfonyl) -4(S) -phenyl-5 (R) -oxazolidine carboxylic acid, 10-deacetyl-7, 10-bis-trichloroacetylbaccatin III 13-yl-ester (VII)

b) Hydrolysis of the Compound of formula (VII) with trichloroacetyl groups in the 7 and 10 positions gives 2- (2, 4-dimethoxyphenyl) -3- (2-nitrothiophenyl) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetylbaccatin III 13-yl-ester (VIII)

c) The compound of formula (VIII) is subjected to acid treatment to obtain 10-deacetyl-N-debenzoyl-taxol (I).

The invention also provides the novel intermediates 2- (2, 4-dimethoxyphenyl) -3- (2-nitrothiophenyl) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetyl-7, 10-bis-trichloroacetylbaccatin III 13-yl-ester (VII) and 2- (2, 4-dimethoxyphenyl) -3- (2-nitrothiophenyl) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetylbaccatin III 13-yl-ester (VIII).

The invention also relates to a process for the preparation of 10-deacetyl-di-7, 10-trichloroacetylbaccatin III, in which the content of the corresponding 7 or 10 mono-trichloroacetyl derivative is less than 0.1% as determined by HPLC, said process comprising subjecting the reaction mixture to silica gel chromatography.

It is another object of the present invention to provide docetaxel having a purity of more than 99% and a pharmaceutical composition comprising the same.

Disclosure of Invention

The present invention relates to a method for synthesizing synthon (I) with high yield and/or high quality. In addition, the process does not require contaminating or difficult to handle reagents such as zinc and hydrofluoric acid.

The method comprises reacting 2- (2, 4-dimethoxyphenyl) -3- (2-nitrobenzenesulfonyl) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid (V)

With 10-deacetyl-di-7, 10-trichloroacetylbaccatin III (VI)

The reaction is carried out to obtain an ester (VII),

synthon (I) is obtained after liberation of the amino and hydroxyl functions.

The compounds of formula (VII) are novel and are another object of the present invention.

2R, 2S oxazolidine acid (V) or mixtures thereof are equally useful in the present synthesis because the chiral center at the 2-position of the oxazoline ring is eliminated from the liberation of intermediate (VII) at the hydroxyl and amino functional groups. In other words, the relative proportions between the diastereomers are such that synthesis is not compromised.

Oxazolidine acid (V) can be easily prepared by acid treatment of the corresponding base salt, the preparation of which is disclosed in WO 03/087077a 1.

The acid (V) is characterized by a significant stability compared to other oxazolidineoic acids; so that it can be easily subjected to esterification with synthon (VI).

Furthermore, after esterification, the liberation of the amino and hydroxyl functions contained in the acid residue can be easily carried out by treatment with an acid without the need to employ drastic conditions.

The taxane synthon (VI) is prepared from the natural metabolite 10-deacetylbaccatin III by esterification of the 7 and 10 positions by treatment with an activated derivative of trichloroacetic acid according to known esterification methods. Preferably, synthon (VI) is obtained by reaction with trichloroacetyl chloride at about 0 ℃ and using pyridine as solvent. Preferably, 10-deacetyl-di-7, 10-trichloroacetylbaccatin III (VI) is purified by silica gel chromatography or equivalent to remove its corresponding 7 and 10-mono-trichloroacetyl esters. The residual amount of said impurities should not exceed 0.1% as determined by HPLC% peak area.

According to the invention, the esterification reaction of (VI) with oxazolidine acid (V) to give (VII) can be carried out in the presence of a condensing agent, e.g. a diimide such as dicyclohexylcarbodiimide and an activating agent, e.g. 4-dimethylamino-pyridine or 4-pyrrolidin-1-ylpyridine, in a solvent selected from the group consisting of: ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran or dioxane; esters such as ethyl acetate, propyl acetate or butyl acetate; aromatic hydrocarbons such as benzene, toluene or o-, m-, p-xylene; or a halogenated aliphatic hydrocarbon such as dichloromethane, chloroform or dichloroethane. It is particularly advantageous to carry out the esterification in methylene chloride at a temperature of about 20 ℃.

Preparation of synthon (I) from ester (VII) requires removal of the trichloroacetyl groups from the 7 and 10 positions and liberation of the amino and hydroxyl functional groups from the oxazolidine residues.

As noted above, amino and hydroxyl functional groups can be readily liberated from oxazolidine residues by acid treatment. In contrast, hydrolysis of trichloroacetic acid esters is conveniently carried out by a weak base treatment, preferably by reaction with ammonium hydroxide.

It has been observed that if the liberation of the amino and hydroxyl functions from the oxazolidine residue is carried out first, a considerable migration of the trichloroacetyl group from the baccatin residue to the free amino function will occur, followed by the formation of a trichloroacetylamino function which can be converted into an amino function only under conditions detrimental to the baccatin skeleton. Thus, the preparation of synthon (I) first requires removal of the trichloroacetoxy groups at the 7 and 10 positions of (VII) to give ester (VIII).

The compounds of formula (VIII) are also novel and are another object of the present invention. Preferably, the treatment with ammonium hydroxide in tetrahydrofuran as solvent is carried out at room temperature to remove trichloroacetic acid groups.

The liberation of the amino and hydroxyl functions by acid treatment is preferably carried out in an alcoholic solution, for example methanol, with aqueous hydrochloric acid at about 20 ℃. After dilution with water and removal of reaction by-products with organic solvents, for example aliphatic hydrocarbons and halogenated aliphatic hydrocarbons, for example n-hexane and dichloromethane, the synthon (I) is isolated by basification of the aqueous phase, extraction with organic solvents, for example dichloromethane or ethyl acetate, concentration and precipitation in aliphatic hydrocarbons, for example n-hexane. The process of the invention provides synthon (I) with a purity higher than 98% without the need for chromatographic purification.

Docetaxel can be conveniently obtained from said intermediate by reaction with di-tert-butyl dicarbonate, with a purity higher than 99%, preferably higher than 99.4%.

The reaction is preferably carried out in a solvent such as an alcohol (methanol, ethanol, isopropanol, preferably ethanol), a chlorinated hydrocarbon (dichloromethane, chloroform, preferably dichloromethane) or a mixture thereof in the absence of a base.

The process is convenient because docetaxel of high purity can be obtained by crystallization from a suitable solvent, preferably ethanol/water and/or acetone/hydrocarbon mixtures, without cumbersome chromatographic purification. Docetaxel obtained using the process of the invention is characterized by a purity higher than 99% (HPLC area%) and by a content of both 7-epidocetaxel and 10-dehydrodocetaxel lower than 0.1% (HPLC area%).

The present invention will now be illustrated in more detail in the following examples.

Examples

Example 1: 10-deacetyl-7, 10-dichloroacetyl baccatin III (VI)

10-deacetylbaccatin III (15g) was treated with a solution of 6.6ml of trichloroacetyl chloride in 60ml of pyridine at 0-5 ℃ for 1 hour with stirring. The mixture was diluted with 100ml of dichloromethane and 100ml of 4N hydrochloric acid. The phases are separated and the organic phase is washed with 100ml of 4N hydrochloric acid and 50ml of saturated aqueous sodium chloride solution. The organic phase is concentrated in vacuo and the residue is taken up in 100ml of toluene. The product (VI) was collected by filtration and dried in vacuo at 50 ℃. The latter was dissolved in CH at 35 ℃₂Cl₂In (80ml) 800g of Kiesegel 60Merck (eluent: CH) were used₂Cl₂) Purifying by column chromatography. The fractions were combined (TLC: CH)₂Cl₂) And checked by HPLC. The total content of mono 7-and 10-trichloroacetylbaccatin III must be less than 0.1%. Precipitation of purified compound (VI) in toluene gave (17.8g, 2)1.4mmol, 660/26/B, A% purity: 99%, yield: 78%).

Example 2: 2- (2, 4-Dimethoxyphenyl) -3- (2-nitrobenzenethiol) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetyl-7, 10-bis-trichloroacetylbaccatin III 13-yl ester (VII)

A solution of 10.3g of (V) in the form of the sodium salt in 100ml of water is cooled to 0-5 ℃ and adjusted to pH 2-3 with 2M sodium hydrogensulfate solution. The reaction mixture was stirred at 0 ℃ for 15 minutes, then CH was added₂Cl₂(70ml), the two phases were separated and the aqueous layer was treated with CH₂Cl₂Extraction was performed once (1 × 50 ml). The organic phases were combined, washed with saturated sodium chloride solution (1X25ml) (360g/l) and over anhydrous MgSO₄(3g, KF 0.12%) dried. After filtration, the solution was concentrated to 100ml at room temperature under vacuum. To this yellow solution was added 12g of (VI), followed by 0.175g (1.42mmol) of Dimethylaminopyridine (DMAP), and after complete dissolution of the reagent, 5.88g of Dicyclohexylcarbodiimide (DCC) was added. The reaction mixture was stirred at room temperature for 1 hour. By TLC (Ethyl acetate/Hexane: 1/2, containing H by spraying₂SO₄(31mL), ammonium molybdate (19g), and (NH)₄)₄Ce(SO₄)₄·2H₂A solution of O (1.9g), water (500mL) and heated at 130 ℃ for 5 minutes for detection) no starting material (VI) was detected. The Dicyclohexylurea (DCU) formed is filtered off and precipitated with CH₂Cl₂(1 × 20mL) washing. The dichloromethane solution was evaporated to dryness to give 24g of (VII).

Example 3: 2- (2, 4-Dimethoxyphenyl) -3- (2-nitrobenzenethiol) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetylbaccatin III 13-yl ester (VIII)

A solution of 24g of (VII) in 100ml of tetrahydrofuran is concentrated under vacuum, and the residue is taken up in 150ml of Tetrahydrofuran (THF) and then concentrated to 100ml under vacuum.

At room temperature, 33% ammonium hydroxide (NH) was added over 5 minutes₄OH, 1.8ml, 30mmol) and stirring the reaction mixture at room temperatureStirring for two hours. TLC of the mixture showed no compound (VII) (ethyl acetate/hexane: 4/3). The solution is concentrated in vacuo and the residue is taken up in 125ml of methanol. The suspension was stirred for two hours. The precipitate was filtered through a sintered glass filter and washed with 10ml of methanol to obtain compound (VIII) (13g, 12mmol, HPLC a% ═ 93%, yield 84%). The mother liquor containing 9.3g of residue was discarded.

Example 4: 10-deacetyl-N-debenzoyl-paclitaxel (I)

A suspension of 260ml of methanol, 13g of (VIII) is treated with 4.2ml of concentrated hydrochloric acid diluted in 130ml of methanol at room temperature with stirring for 30 minutes. The reaction mixture was stirred at room temperature for four hours and the suspension became a clear yellow solution. TLC showed no compound (VIII) in the mixture (ethyl acetate/hexane: 4/3). The solution was slowly diluted with 350ml of water (to avoid precipitation) and the homogeneous solution was stirred at room temperature for 30 minutes. 200ml of dichloromethane were added, the two phases were separated and the aqueous layer was extracted again with dichloromethane (2X 100 ml). The organic phase was removed. The water-alcohol phase is cooled to 0-5 ℃ and diluted with 100ml of dichloromethane. Vigorously stirred at 0-5 deg.C and concentrated ammonia (3.1ml, NH) was added dropwise₄OH) until the pH reaches 7-8 (temperature will rise by 1 degree). The two phases were stirred at the same temperature for 20 minutes, then the phases were separated and the aqueous layer was extracted with dichloromethane (5X 100 ml).

The combined organic layers were concentrated to 100ml in vacuo and the product crystallized upon stirring at room temperature. The precipitate was filtered through a sintered glass filter and dried overnight under vacuum at 40 ℃ to obtain 7.5g of the title compound.

Example 5: preparation of docetaxel

Compound (I) (16g, HPLC analytical purity: 90.57%, 20.49mmol) was dissolved in a 1: 1 mixture of anhydrous ethanol and dichloromethane (320ml), and di-tert-butyl dicarbonate (BOC) was added to the pale yellow solution₂O is in CH₂Cl₂Solution of (5.27 g, 24.18mmol in 5ml of CH)₂Cl₂). After the addition was complete, the reaction mixture was stirred at room temperature for 16 hours. TLC displayShows no compound (I) (CH)₂Cl₂MeOH: 9/1, using a mixture containing sulfuric acid (31ml), ammonium molybdate (19g) and (NH)₄)₄Ce(SO₄)₄·2H₂A solution of O (1.9g) in 500ml of water was sprayed and heated at 130 ℃ for 5 minutes for detection). The methylene chloride was distilled off, and 0.39ml of acetic acid was added to the solution. The acidic ethanol solution was heated at 50 ℃ and 320ml of pure water was added dropwise. The mixture was allowed to stand at 50 ℃ for 1 hour and then at room temperature for 2 hours. The precipitate was filtered through a sintered glass filter and transferred to a vacuum drying oven where it was kept under vacuum at 40 ℃ overnight to obtain 16.75g of semi-purified docetaxel and 1g of mother liquor, which was discarded.

The crude product was crystallized twice: the semi-purified docetaxel was dissolved in 160 ml of 95% ethanol at 50 ℃ and 0.39ml of acetic acid was added. After adding 320ml of pure water, the mixture was left at 50 ℃ for 1 hour and then at room temperature for 2 hours. The precipitate was filtered through a sintered glass filter, transferred to a vacuum drying oven, and left overnight in vacuum at 40 ℃ in the vacuum drying oven to obtain 15.25g of docetaxel and 0.4g of mother liquor, which was discarded. The second crystallization was carried out by redissolving the product in 150ml of acetone at 30 ℃ and adding 150ml of heptane. The mixture was left at room temperature for 3 hours. The precipitate was filtered through a sintered glass filter, transferred to a vacuum oven and placed in vacuum at 40 ℃ overnight to yield 13.9g of docetaxel (HPLC purity greater than 99.4%, < 0.1% 7-epidocetaxel and < 0.1% 10-dehydrodocetaxel).

Example 6: alternative scheme for preparing docetaxel

De-BOC docetaxel (30.0g, 42mmol, 98% HPLC purity, 0.2% 7-epi isomer) was placed in a 1l reactor and 60ml dichloromethane, 150ml absolute ethanol and 73. mu.l glacial acetic acid (3% mol) were added at 25 ℃ to obtain a suspension.

BOC anhydride (11.0g, 51mmol) dissolved in 30.0ml DCM was added dropwise at 25 ℃ to give a clear solution after the addition was complete.

After 3 hours, the reaction was quenched with glacial acetic acid (0.7ml, 30% mol) and the dichloromethane was distilled off in vacuo at 30 ℃. Then 90ml of absolute ethanol were added and distilled off under the same conditions.

The clear solution was heated to 50 ℃ and 570ml of water were added dropwise over about 3 hours. The suspension was stirred at 50 ℃ for 1 hour, then cooled to 25 ℃ over 1 hour and stirred at this temperature for 16 hours.

The white solid was filtered and washed twice with a solution of 40ml water and 18ml absolute ethanol.

The crude starting material was charged to the reactor with 250ml ethanol and 630. mu.l glacial acetic acid.

The mixture was heated at 50 ℃ to dissolve it sufficiently. 570ml of water were added dropwise over two hours. The mixture was then cooled to 25 ℃ over 1 hour, after 90 minutes, the suspension was filtered on a Guschner funnel P3 and washed once with a solution of 40ml of water and 18ml of absolute ethanol.

Docetaxel was obtained as a white solid, dried under vacuum at 55 ℃ for 16 hours to obtain a dry solid with a final weight of 32.6 g.

The crude docetaxel (5.0g, 6.2mmol) was added to a 500ml reactor and dissolved in acetone (50ml) at 50 ℃.

N-heptane (50ml) was added slowly over a period of about one hour at 50 ℃. The suspension thus obtained was stirred at 50 ℃ for 1 hour, then cooled to 25 ℃ and stirred at the same temperature for 16 hours.

The suspension was filtered on a funnel of gooch P3, washed once with n-heptane (15ml) and dried under vacuum at 55 ℃ for 16 hours to obtain 4.40g of docetaxel as a white solid (89% yield, > 99.5% HPLC purity, < 0.10% 7-epi docetaxel and < 0.10% 10-dehydrodocetaxel).

Drawings

Figure 1 XRD diffractogram of the sample prepared by the method of example 5.

FIG. 2 DSC thermogram of sample prepared by the method of example 5.

Claims (9)

1. A process for the preparation of 10-deacetyl-N-debenzoyl-paclitaxel (I),

   which comprises the following steps:

   a) 2- (2, 4-dimethoxyphenyl) -3- (2-nitrobenzenethiol) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid (V)

   With 10-deacetyl-di-7, 10-trichloroacetylbaccatin III (VI)

   The reaction is carried out to obtain 2- (2, 4-dimethoxyphenyl) -3- (2-nitrobenzenesulfonyl) -4(S) -phenyl-5 (R) -oxazolidine carboxylic acid, 10-deacetyl-7, 10-bis-trichloroacetylbaccatin III 13-yl-ester (VII)

   b) Hydrolysis of the Compound of formula (VII) with trichloroacetyl groups in the 7 and 10 positions gives 2- (2, 4-dimethoxyphenyl) -3- (2-nitrothiophenyl) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetylbaccatin III 13-yl-ester (VIII)

   c) The compound of formula (VIII) is subjected to acid treatment to obtain 10-deacetyl-N-debenzoyl-taxol (I).
2. 2. The process according to claim 1, wherein step a) is carried out in a solvent selected from ethers, esters, aromatic hydrocarbons or halogenated aliphatic solvents.
3. 3. The process according to claim 2, wherein the aliphatic halogenated hydrocarbon is dichloromethane.
4. 4. A process according to any one of claims 1 to 3, wherein step a) is carried out in the presence of a condensing agent and an activating agent.
5. 5. The process of claim 4 wherein the condensing agent is dicyclohexylcarbodiimide and the activating agent is 4-dimethylamino-pyridine.
6. 6. A process according to any one of claims 1 to 3, wherein step b) is carried out with ammonium hydroxide in tetrahydrofuran as solvent.
7. 7. A process according to any one of claims 1 to 3, wherein step c) is carried out with a solution of hydrochloric acid in methanol.
8. 2- (2, 4-Dimethoxyphenyl) -3- (2-nitrobenzenethiol) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetyl-7, 10-bis-trichloroacetylbaccatin III 13-yl ester (VII)
9. 2- (2, 4-Dimethoxyphenyl) -3- (2-nitrobenzenethiol) -4(S) -phenyl-5 (R) -oxazolidinecarboxylic acid, 10-deacetylbaccatin III 13-yl ester (VIII)